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Figure 8.2 Sketch. Illustration of qualitative differences between the full flow separation (a) and
separation due to wave breaking (b). Solid line signifies the surface water wave. Positions of crest,
trough and windward face of this wave are indicated with vertical lines. Dashed line demonstrates
the induced pressure wave. Vertical scales are arbitrary, vertical dimensions of the pressure waves
in the two subplots are scaled relative to the water wave. Figure is reproduced from
Babanin
et al.
(
2007b
)
©
American Meteorological Society. Reprinted with permission
steepnesses (
Peirson &Garcia
,
2008
; presentation of Savelyev
et al.
at WISE-16, Ensenada,
Mexico, 2009; see also
Section 9.1.3
). In discussion of
Figure 8.4
below in this section, it
is also demonstrated that, relatively, the enhancement effect decreases once the full flow
separation starts to occur.
The wind-input source function proposed in
Donelan
et al.
(
2006
) was parameterised
by wave steepness and degree of separation, in addition to the traditional wind-forcing
properties. This formulation was shown to be in agreement with, and in fact to be able to
reconcile, previous field and laboratory data obtained for a variety of conditions in terms
of wind forcing and wave steepness. Hence the steady-state strong-forcing conditions dur-
ing the Lake George experiment provided a possibility to define a generalised wind-input
source function
S
in
in
(2.61)
that is suitable for parameterising wave amplification through
wind action for a wide range of conditions.
Since wave breaking can be very frequent (up to 60% in
Babanin
et al.
(
2001
)), the
breaking-induced separation has the potential to produce a noticeable enhancement of such
atmospheric input to the waves and the function
S
in
. Apart from the wave growth as such,
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